SOCIAL AND ECONOMIC IMPACT OF GLOBAL CHANGE ON SOME TROPICAL FISHERIES Ernesto A. Chávez & José Luis Castro-Ortiz CICIMAR, Instituto Politécnico Nacional.

SOCIAL AND ECONOMIC IMPACT OF GLOBAL CHANGE

ON SOME TROPICAL FISHERIES

 Ernesto A. Chávez & José Luis Castro-Ortiz 

CICIMAR, Instituto Politécnico Nacional. La Paz, MEXICO [email protected]

One of the main problems in fisheries management is linked to accurate assessment of exploited stocks and in the provision of realistic advice.

The main constrain in this task is the strong influence of environment upon recruitment of new generations, imposing high uncertainty to the

estimations of stock size

Clear discrimination of changes in stock size caused by the fishing intensity from those caused by climatic change is a task difficult to accomplish, especially in those fisheries based on highly variable short-lived stocks strongly linked to annual variability

Only the El Niño Southern Oscillation (ENSO), with a period of to five-to-seven year oscillations, has been recognized for several decades, to have a significant impact on many fisheries of West America

Many species repond to climate shifts. However, the response to climatic change is not the same in all cases, some species respond with different sign and intensity to regime shifts

Influence of environment has been perceived intuitively in short-lived species like sardines, and anchovy, rather difficult to assess by traditional models applied to fisheries, because their sudden changes in recruitment rate and natural mortality, strongly influenced by the environment, are difficult to evaluate

Abrupt climatic shifts have been recently discoveredThese abrupt shifts have had strong influence in ecosystems worldwide There is an implicit thought that the relative stability of tropical environments are not quite susceptible to show the effects of climatic change

GOAL

To examine the response of main fisheries of West Mexico in the context of several indices of climate change, identifying their response against climate shifts

THE INDICES OF CLIMATE OCEAN

Some indicators of climatic processes describing the major climate and ocean systems are a good evidence of the impact of climate change on biological systems

Fisheries may be the best source of information available to understand the nature and intensity of these impacts on exploited stocks

The main oceanic climate indices(After several sources. Y axis is the Cumulative Summation of anomalies)

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1950 1960 1970 1980 1990 2000

LOTI CTI ALPI PDO SOI NAOI

THE IMPACT OF CLIMATE CHANGE ON FISHERIES

Sixteen fisheries of West Mexico were selected

Their overall biomass landed accounts for nearly 570,000 metric tonnes (mean for 1995-1999) representing 78% of total landings of West Mexico

CLIMATE CHANGE AND FISHERIES

YIELD t, WEST MEXICO (Mean 1995-99)

0.E+00 1.E+05 2.E+05 3.E+05 4.E+05

Abalones

Snappers, jobfishes

Mullets

Californian anchovy

Skipjack tuna

Brown seaweeds

Penaeus shrimps

California pilchard

Landing data were analyzed as normalized departures from five-year moving mean values each year. This way, decadal patterns of high or low recruitment are shown and shifts expressed as response of stocks to climate change are displayed

CLIMATE SHIFTS AND THE FISHERIES  The most striking characteristic of the indices of climate change described above, is the shift occurring by the middle of the 70’s

Three main patterns of impact of the climate change are identified on the fisheries:

1. A response to the shift in middle 70,s. 2. A shift in 1989, approximately3. Species that apparently respond to El

Niño-La Niña events

1. Impact of the shift of the middle seventies on:

Abalone California pilchardSharks JacksSkipjack tuna Red and brown seaweeds

IMPACT OF THE SHIFT OF THE MIDDLE SEVENTIES

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1950 1960 1970 1980 1990

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Abalone

CA Pilchard

Sharks

Jacks

Red seaweeds

Skipjack tuna

2. The shift of the Middle 80´s  

Characterized by a moderate negative response before the middle 80’s, then an abrupt response leading to spectacular increases in catches afterwards:

Crabs Giant squid

Groupers Chub mackerel

The shift of the Middle 80´s

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1950 1960 1970 1980 1990

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Crabs

Giant squid

Groupers

Chub mackerel--------->

3. Response to El Nino events 

Is well known as warm above normal temperatures followed by cold periods occurring every five to seven years

Fisheries impacted :

Shrimp Spiny lobster Snappers Mullets

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1950 1960 1970 1980 1990

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Shrimp

Spiny lobster

Snappers---

Mullets

Brown seaweeds--o--

Response to El Niño Events

A clear pattern of response to climate change, although not identified, is

observed in the anchovy

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1950 1960 1970 1980

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THE HUMAN DIMENSION AND THE GLOBAL CHANGE 

Climate regime and shifts impose drastic effects on marine ecosystems

Its knowledge opens a new perspective regarding our understanding of environmental processes ruling the

dynamics of exploited species

A clear discrimination between changes in stock size caused by the fishing intensity and those caused by climatic change makes it a task rather difficult to accomplish

Impact of climate change in the long term may be one of the main factors constraining the possibility of accurate estimation of the stock biomass when planning fishing activities for the next season is required

Its knowledge will allow to understand the sources of noise specially related to estimates of recruitment rates of exploited stocks, but it may not be a good help trying to input this knowledge directly into the issues of fisheries management in the short term

Adaptive management is a process by which a continuous stock assessment is carried on year by year, to reorient the exploitation policies for the next season

Hence, there would be no place for long term considerations of climate change effects beyond those related to long term

planning

Under a climate regime imposing low recruitment and biomass levels to a fishery, it is not likely to restore the stock to levels similar to those when yields were very high

This is the case of abalone, whose yields were two orders of magnitude higher four decades ago

The best management strategy applied nowadays, would not be able to restore the stock size to those high levels in the short term

The case of the California pilchard is analogous, but with opposite sign

According to the positive effect of climate change that it displays, it is suspected that it might be difficult to expect a significant impact by the fishing intensity

CONCLUSION

Within the framework of climate change

the human impact as the responsible one for the depletion or restoration of exploited stocks is perceived as the most likely effect in short term

Overexploitation may play an important role depleting the stocks, but in the long term, the main role is played by the climate